The present invention relates to an enclosure for an air aspirating machine, particularly for a compressor for a fuel cell drive. The invention further relates to an assembly, which, in addition to the aforementioned enclosure, also comprises the air aspirating machine.
It is known to provide devices that emit structure-borne noise with an enclosure, which dampens the noise emitted by these devices and also, if lined with absorption material, absorbs it. These enclosures are preferably made of acoustically insulating materials that do not let the energy pass through to the surroundings.
Such enclosures, however, require additional clearance. In automotive engineering the sound emitting machines, for instance the internal combustion engine or the compressor for a fuel cell drive, are arranged in tight spaces. If an enclosure as described is provided, the necessary clearance must be obtained, e.g., by reducing acoustically effective volumes in the inlet path of the air aspirating machine. In most cases, therefore, the enclosure represents an acoustic compromise.
It is the object of the present invention to provide an enclosure for an air aspirating machine, or an assembly comprising such an enclosure and the air aspirating machine, while making optimal use of the volume that is used to dampen the noise.
These and other objects are achieved in accordance with the present invention by providing an enclosure for an air aspirating machine which draws in air along an air intake path extending through a wall of the enclosure, wherein the enclosure completely encompasses the air aspirating machine, and the enclosure is sealed relative to its surroundings so as to form a resonant cavity which communicates with the air intake path of the air aspirating machine.
In accordance with a further aspect of the invention, the objects are achieved by providing an assembly comprising an air aspirating machine and an enclosure in which the air aspirating machine is installed, wherein the enclosure is sealed relative to its surroundings so as to form a resonant cavity, the resonant cavity communicating with an air intake path of the air aspirating machine, and the air aspirating machine having an air intake which extends through a wall of the enclosure.
The enclosure according to the invention completely encompasses the air aspirating machine. This makes it possible to achieve optimal sound insulation with respect to the structure-borne noise emitted by the air aspirating machine. The enclosure according to the invention is characterized in that it is completely sealed off from the surroundings, so that the volume it encloses cannot communicate with the surroundings. This creates a resonant cavity that can communicate only with the air intake path of the machine. The volume encompassed by the enclosure can thus be simultaneously used as an acoustically effective volume for the inlet noise of the air aspirating machine. Thus, the enclosure has a dual function. The sound damping and sound absorbing properties of the enclosure material and the resonator characteristics of the enclosed volume are used simultaneously.
The enclosed volume will be quite large compared to the volumes that are usually available for acoustic measures in the intake path. It is therefore particularly suitable for reducing low-frequency noise components in the intake noise. The structural components provided within the enclosure result in a complex geometry of the resonator volume. This has a broadband noise reduction effect when considered over the frequency of the intake noise.
The enclosure according to the invention is particularly suitable for compressors, such as those used in fuel cell drives. The requirements for high volumetric efficiency and the reduction in the air""s ability to absorb moisture lead to the selection of compressors with a very high power density. As a function of the type of construction, these compressors emit a loud noise both at the intake opening and through the housing walls. The enclosure according to the invention can effectively dampen both the structure-borne noise emitted through the housing walls of the compressor and the noise in the intake opening. This makes it possible to adjust the compressor noise to the noise level of the remaining functions of the fuel cell drive, so that it is not noticeable as a disagreeable and disturbing noise.
In accordance with one specific embodiment of the invention, the air intake that leads into the enclosure is provided with an air filter. Filtering the air is necessary, for instance, in internal combustion engines and fuel cell drives. The air filter is generally provided in a housing, which as an acoustic volume per se helps dampen the intake noise. The housing can either be separate or integrated into the enclosure or the volume encompassed by the enclosure.
A further advantageous embodiment of the invention is obtained if other sound emitting components are accommodated within the enclosure in addition to the air aspirating machine. This reduces the overall noise of the functional group, which, for instance, represents a motor vehicle. In this case, the enclosure acts in its sound damping and S absorbing capacity. Examples of other noise emitting components are turbochargers or electric motors.
One advantageous embodiment of the invention provides that the resonant cavity operate as a series resonator. This means that the air inlet opens out into the volume formed by the enclosure, and the air aspirating machine for its part has an intake opening. Thus, the air drawn in by the air aspirating machine must flow through the resonant cavity.
Another option provides that the resonator be used as a parallel resonator. In this case the air intake path from the air inlet to the air aspirating machine essentially forms a connected duct system, which must have some openings to the resonant cavity in order to be able to communicate with the resonant cavity.
Between the described modes of action as a series or as a parallel resonator, it is, of course, possible to provide other resonators in which the described effects are superimposed. It is feasible, for instance, to arrange the inlet opening of the air aspirating machine and the outlet opening of the air intake so close together that there is only a gap between the two openings leading to the resonant cavity.
It is advantageous to equip the air aspirating machine with a safety filter, which may be arranged on the air inlet of the air aspirating machine located within the resonant cavity. This safety filter can eliminate any dirt particles, which, due to a leak in the enclosure, may reach the resonant cavity despite prior filtering of the air drawn in. This increases the reliability of the entire unit and reduces the tightness requirements of the enclosure, respectively.
Another option to protect the air aspirating machine from dirt particles in the resonant cavity is to arrange a sound permeable wall in the air intake path, which communicates with the resonant cavity. This assures acoustic communication of the resonant cavity with the air intake path. The sound permeable wall can be made impermeable for any dirt particles and thus assumes a function similar to a safety filter.
The sound permeable wall can even be made absolutely air-tight. For instance, a membrane that is arranged in the walls of the intake path can transmit the sound vibrations from the interior of the intake path to the resonant cavity. Such a membrane is thus sound permeable even though there is no air exchange between the resonant cavity and the air intake path.
The sound permeable wall can be formed, in particular, by a flexible hose, which is installed as a line segment in the air intake path. Hoses with a foam-like structure, which are applied to a support hose, e.g., made of a woven fabric, are preferably used for this purpose. Such hoses represent a comparatively inexpensive semi-finished part, which can be readily integrated in the air intake path. This makes it possible to use the resonant cavity in the enclosure without any risk to the air aspirating machine. The arrangement of the hose furthermore increases the degree of geometric design freedom in arranging the air aspirating machine within the enclosure.
These and other features of preferred embodiments of the invention, in addition to being set forth in the claims, are also disclosed in the specification and/or the drawings, and the individual features each may be implemented in embodiments of the invention either individually or in the form of subcombinations of two or more features and can be applied to other fields of use and may constitute advantageous, separately protectable constructions for which protection is also claimed.